1. Field of the Invention
The present invention relates to a traffic control device for protecting resources in a network in, for example, a private asynchronous transfer mode (ATM) network.
2. Description of the Related Art
Recently, broadband switching units have been widely developed and are expected to be used more popularly in a broadband network operated by an ATM system. The ATM broadband network is also expected to be adopted in a private network.
The broadband switching unit in a public ATM network is designed according to the standard specification determined by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) whereas the broadband switching unit used in the private ATM network need not be designed according to the specification.
The above described discussion about the ATM network is also effective in a conventional narrow band-integrated services digital network (N-ISDN). That is, a number of switching units used in a private N-ISDN have some useful functions in addition to the capabilities of the switching units used in a public N-ISDN, or are provided with the capabilities of the switching units used in a public N-ISDN by substitute units.
A traffic control function protects resources in a network. It is realized by a use amount parameter control system in the public ATM network. Then, it is very important in the private ATM network to effectively realize the capabilities of the use amount parameter control system in the public ATM network.
FIG. 1 shows a conventional technology of the use amount parameter control function currently used in the broadband ATM switching unit in the public ATM network.
A call reception control unit 103 receives the declaration of a declared band. Then, the call reception control unit 103 obtains from a band management unit 104 a space band in a circuit used by a user from among output circuits 106 connected to an ATM switch (self-routing switch) 101. The call reception control unit 103 then compares the space band with the user-declared band to determine whether or not a request to set a call is accepted from the user. If it is accepted, the call reception control unit 103 sets in a usage parameter control unit 102 provided on an input circuit 105 connected to the ATM switch 101 the declared band for the user who issued the request.
The usage parameter control unit 102 is realized by a dedicated hardware and monitors for each connection of a user of the input circuit 105 connected to the usage parameter control unit 102 whether or not a band of each connection is larger than a declared band corresponding to the connection. If the usage parameter control unit 102 detects a connection of a band larger than the declared band, it normally discards the cell of the connection as illegal.
As a result, as shown in FIG. 2, the band of a connection is controlled at the input circuit 105 such that it should be smaller than the declared band for the connection, thereby preventing congestion in the ATM switch 101 and the output circuit 106 from occurring.
A band is declared by a user using a peak band which is used the most frequently in all bands used for the services to the user. The usage parameter control unit 102 also manages bands using the peak band. Practically, if a user connected to an interface having a transmission rate of 150 Mb/s (megabits/second) tries to provide a communications service, the user declares 100 Mb/s as the most frequently used band in his or her communications services as shown in FIG. 3 to the call reception control unit 103 shown in FIG. 1. The usage parameter control unit 102 performs its control on each connection such that the peak band declared for each connection is larger than the peak band currently used by the connection.
Described below is the conventional technology of the use amount parameter control system practically realized by the usage parameter control unit 102 shown in FIG. 1.
FIG. 4 shows the case where the use amount parameter control function performed by the usage parameter control unit 102 is realized by the conventional system called a leaky bucket system.
In FIG. 1, a cell received from the input circuit 105 is sequentially stored by a buffer 401 shown in FIG. 4 provided in the usage parameter control unit 102. The usage parameter control unit 102 reads for each connection the cell stored in the buffer 401 at a rate corresponding to the declared band for the connection, and outputs it to the ATM switch 101 (FIG. 1).
As a result, shown in FIG. 4 is the relationship between input and output cells to and from the usage parameter control unit 102 for a connection. Assuming that the number of cells remaining in the buffer 401 allowed corresponding to a declared band of one connection is three, an input cell is discarded when the number of input cells to the connection reaches four in the buffer 401 (the ninth input cell in FIG. 4).
FIG. 5 shows the case where the use amount parameter control function performed by the usage parameter control unit 102 shown in FIG. 1 is realized by the conventional system called a sliding window system.
A window is set for each connection. The window has a given time length Ts by which it is shifted at the shortest cell time intervals. When the number of input cells N in the window exceeds the number of cells Ns in the window allowable for the declared band for each connection at each monitor point, the latest input cell in the window is discarded as an illegal cell.
FIG. 6 shows the case in which the use amount parameter control function performed by the usage parameter control unit 102 is realized by the conventional system called a jumping window system.
With this system, a plurality of windows (three in the example shown in FIG. 6) shown in FIG. 5 are simultaneously set in the time direction. The monitor results of these windows are simultaneously determined to check whether or not an input cell is illegal.
In each of the above described systems shown in FIGS. 4 through 6, further proposed is a system in which a difference can be allowed in cell arrival time depending on, for example, a route in a network.
FIGS. 7A and 7B show using cell loss priority (CLP) information the conventional system which realizes the use amount parameter control function performed by the usage parameter control unit 102 shown in FIG. 1.
The CLP is 1-bit information added to the header of a cell. A user can use the CLP to assign priority to each cell. For example, assuming that the information to be transmitted in a cell is image information, an image cannot be regenerated if, for example, the frame information is lost. Therefore, a cell transmitting image frame information is assigned a high priority of CLP=0. On the other hand, for example, image information such as that indicating the background of a scene is assigned a low priority of CLP=1 because it can be interpolated from the adjacent frames.
The usage parameter control unit 102 shown in FIG. 1 divides an input cell for two routes according to CLP values added to the input cell through a selector 701 as shown in FIG. 7A. The band of an input cell divided by the selector 701 and assigned the high priority (CLP=0) is monitored for each connection by a first control unit 702 according to the above described systems shown in FIGS. 4 through 6, and an illegal cell is discarded. The input cell assigned the high priority (CLP=0) and not discarded by the first control unit 702 is mixed by a mixing unit 703 with the input cell divided by the selector 701 and assigned the low priority (CLP=1). Then, the bands of the mixed input cells are monitored for each connection by a second control unit 704 according to the above described systems shown in FIGS. 4 through 6, and an illegal cell is discarded. In each connection, the input cell assigned the low priority (CLP=1) is discarded before the input cell assigned the high priority (CLP=0).
The control system shown in FIG. 7B can also be adopted. In this case, if the input cell divided by the selector 701 and assigned the high priority (CLP=0) is determined to be illegal by the first control unit 702, then the illegal cell is not discarded, and the CLP value of the input cell is forced to be rewritten into 1 indicating the low priority. The input cell is mixed with the input cell divided by the selector 701 and assigned the low priority (CLP=1).
According to the above described control systems, determined is a cell to be discarded for each connection according to the priority assigned to each cell.
The conventional use amount parameter control in the public ATM network should be conducted for each connection, that is, for each virtual path identifier (VPI) and virtual channel identifier (VCI) added to the header of a cell. However, in a broadband switching unit used in the public ATM network, a great number of users are assigned to a single input circuit 105 (FIG. 1), and the transmission rate of the input circuit 105 is as high as 150 Mb/s. Therefore, the usage parameter control unit 102 shown in FIG. 1 cannot perform a realtime cell monitoring process unless realized by dedicated hardware.
Thus, introducing the capabilities of the use amount parameter control function to the switching unit of a private ATM network generates the problem of an increased-cost and large-scale switching unit.
Furthermore, since a private ATM network can be operated according to a given standard based on an agreement and reliability among users connected over the network and does not need the strict cell monitoring function required by the switching unit in the public ATM network, the introduction of the capabilities of the use amount parameter control function to the switching unit of the private ATM network could generate a functional waste.
However, a connection of a user who requests communications frequently to an unreasonable extent should be deleted in any private ATM network. Moreover, resources in a network should be appropriately protected in a private ATM network because a cell may erroneously enter the network due to an unintentional malfunction of, for example, a terminal unit.